Jurors moved a step closer toward sentencing James Holmes to death for his Colorado cinema attack, taking less than three hours to reject arguments that his mental illness means he should not die.

The decision clears the way for one last attempt from both sides to sway the jury, with testimony from victims about their suffering and more appeals for mercy for the man convicted of murdering 12 people and trying to kill 70 more during the 2012 assault at a Batman film.

Holmes, his reactions dulled by anti-psychotic drugs, stood as ordered and appeared emotionless as Judge Carlos Samour read the decisions.

Robert and Arlene Holmes held hands, their fingers interlaced, and directed their eyes at the floor. With each unanimous "yes," it became ever more clear that jurors believe their son's crimes outweighed their testimony. She began to cry, and her husband held out a box of tissues.

More tears flowed in the gallery. Rena Medek began silently sobbing when the judge read the name of her 23-year-old daughter Micayla.

Ian Sullivan, the father of Holmes' youngest victim, six-year-old Veronica Moser-Sullivan, closed his eyes when her name was read. Veronica's grandfather, Robert Sullivan, glared at Holmes and nodded his head softly.

The jury was told to return to court in Centennial today for the final phase. Then, the nine women and three men will finally decide whether Holmes, 27, a former neuroscience student, should receive a lethal injection, or spend life in prison without parole.

The same jury swiftly rejected Holmes' insanity defence, deciding that he was capable of telling right from wrong when he carried out the attack in the Denver suburb of Aurora on July 20, 2012.

Their quick decision raised expectations that they will choose a death sentence after what prosecutors estimate will be two or three more days of testimony from survivors.

But legal experts said there is no way to predict that final decision.

Monday's preliminary verdict was highly technical. They found simply that Holmes' mental problems and the portrait his lawyers painted of a kinder, gentler younger man did not outweigh the horrors of his calculated attack on defenceless cinema-goers.

This next stage can be more challenging for each juror, and to choose capital punishment, they must be unanimous, Denver defence lawyer Dan Recht said.

The defence had argued mental illness reduced Holmes' "moral culpability," and that his personal history made him worthy of mercy. They said it was schizophrenia, not free will, that drove him to murder.

They called his former teachers, friends, sister and parents, who said "Jimmy" had been a friendly child who withdrew socially as he grew older.

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